This invention relates to air source heat pumps, and especially to air source heat pumps suitable for use in normally colder climates. This invention is a modification and improvement to the inventions in prior U.S. Pat. Nos. 6,276,148 and 5,927,088 in that this invention presents a somewhat simpler and less expensive air source heat pump system. The entire contents of my prior U.S. Pat. Nos. 6,276,148 and 5,927,088 are incorporated herein by reference.
Heat pump capacity is understood in the art to be the amount of heat per unit time delivered by a heat pump system. An effective heat pump system must deliver adequate capacity with low or falling outdoor temperature, while avoiding the delivery of too much capacity when the outdoor temperature warms up. Heat pumps that are designed to deliver sufficient capacity at very cold outdoor temperatures may have the inherent problem of delivering too much capacity when the outdoor temperature warms up, because more energy is available to be obtained from the warmer outdoor air. This may cause system inefficiencies as the system heat exchangers become overloaded and compressor power consumption rises to inefficient levels. In extreme cases, safety controls may cause the compressor to stop running.
My prior U.S. Pat. Nos. 6,276,148 and 5,927,088 disclose systems for adjusting capacity in response to decreases and/or increases in outdoor ambient temperature. This involves primary and booster compressors connected in series and a microprocessor which responds to a sensed parameter commensurate with outdoor ambient air temperature to allow sequences of compressor operation for capacity levels consistent with heating and/or cooling requirements and consistent with efficient and safe operation of the system. While the systems of my prior patents are effective for their intended purpose, and particularly for use in very cold climates, a need exists for a simpler and less expensive system.